RO 5126766

Ro 5126766 is a first-in-class dual MEK/RAF inhibitor that allosterically inhibits BRAFV600E, CRAF, MEK, and BRAF (IC50: 8.2, 56, 160 nM, and 190 nM, respectively).

Signaling Pathways >> MAPK/ERK Pathway >> MEK

Research Areas >> Cancer

MEK:160 nM (IC50)

BRafV600E:8.2 nM (IC50)

Braf:190 nM (IC50)

CRAF:56 nM (IC50)

Ro 5126766 (RO5126766) is an allosteric inhibitor that binds directly to MEK and prevents its phosphorylation by RAF through the formation of a stable RAF-MEK complex. Ro 5126766 inhibits both the phosphorylation of MEK by RAF and the activation of ERK by MEK. In cell-free MEK and RAF kinase assays, Ro 5126766 effectively inhibits activation of ERK2 by MEK1 with an IC50 of 160 nM (SD=±0.043) and inhibits the phosphorylation of MEK1 protein by BRAF (IC50=190 nM, SD=±0.003), BRAFV600E (IC50=8.2 nM, SD=±0.0015), and CRAF (IC50=56 nM, SD=±0.016). Ro 5126766 effectively inhibits both MEK and ERK phosphorylation in a panel of human tumor cell lines including KRAS/HRAS and BRAF mutant cell lines and KRAS/HRAS and BRAF wild-type cells[1]. In order to investigate whether the mevalonate pathway affects the sensitivity to MEK inhibitors, human breast cancer MDA-MB-231 cells harboring KRAS and BRAF mutations are treated Ro 5126766 (CH5126766), with or without statins, which inhibits HMG-CoA reductase, the rate-limiting enzyme in the mevalonate pathway. The combined treatment of Ro 5126766 with Fluvastatin demonstrates more significant reduction in cell growth in a dose-dependent manner than the single treatment of Ro 5126766. The marked combined effects of Ro 5126766 at 40 nM and Fluvastatin at 0.3 μM is also confirmed on the suppression of the colony formation of the cells[2].

In KRAS-mutant xenograft models, Ro 5126766 (RO5126766) inhibits growth and causes tumor regressions more effectively than another allosteric MEK inhibitor, PD0325901. Preclinical data from a series of human tumor mouse xenograft models indicates an ED50 for Ro 5126766 of 0.03 to 0.23 mg/kg and an ED90 of 0.15 to 1.56 mg/kg. These effective doses are associated with target trough concentrations of 17 to 133 ng/L and 87 to 901 ng/mL, respectively. [1]. In this experiment, Ro 5126766 (CH5126766) or PD0325901 is administrated at their maximum tolerated dose (MTD) in the HCT116 model (1.5 and 25 mg/kg, respectively). These doses inhibit pERK and ERK signaling output at similar degrees in the tumors from the drug-treated mice at 4 hours from the first drug administration. Moreover, in HCT116 models, the ED50 for Ro 5126766 and PD0325901 are 0.056 and 0.80 mg/kg, respectively. Therefore, the doses used for this experiment are 26.8- and 31.3-fold higher doses than the 50% effective doses, respectively. Daily oral administration of either drug causes significant tumor regression of each these tumors. However, whereas inhibition of tumor growth is maintained for the entire 28-day treatment period in Ro 5126766-treated mice, tumor models receiving PD0325901 become refractory after 10 days of treatment[3].

The number of viable cells is assessed with a Cell Counting Kit-8 assay. Human breast cancer MDA-MB-231 cells, human melanoma SK-MEL-28 cells, and human non-small cell lung cancer A549 cells are seeded at a density of 2,000 cells per well in 96-well plates and incubated for 24 h, and then treated with Ro 5126766 (10, 20, 40, and 80 nM) for 72 h. After a further 4 h incubation with the kit reagent, the absorbance at 450 nm of the samples is measured using a multi-plate reader[2].

Mice[3] Female BALB-nu/nu mice (CAnN.Cg-Foxn1nu/CrlCrlj nu/nu) are given access to standard mouse chow and water ad libitum. A total of 5×106 (HCT116) or 1×107 (Calu-6 and COLO205) tumor cells per mouse are injected subcutaneously into the right flank of the 7- to 9-week-old mice. When tumor volume reaches to 200 mm3 (day 0), the mice are randomized and vehicle [5% DMSO and 10% 2-hydroxypropyl-β-cyclodextrin (HPCD) solution in distilled water], Ro 5126766 (1.5 mg/kg or 2.0 mg/kg) or PD0325901 (25 mg/kg) is administered orally once a day. Drugs are administrated at the maximum tolerated dose (MTD). Tumor growth inhibition (TGI) is calculated. The value of the 50% effective dose (ED50) for each compound is calculated[3].

[1]. Martinez-Garcia M, et al. First-in-human, phase I dose-escalation study of the safety, pharmacokinetics, and pharmacodynamics of RO5126766, a first-in-class dual MEK/RAF inhibitor in patients with solid tumors. Clin Cancer Res. 2012 Sep 1;18(17):4806-19.

[2]. Iizuka-Ohashi M, et al. Blockage of the mevalonate pathway overcomes the apoptotic resistance to MEK inhibitors with suppressing the activation of Akt in cancer cells. Oncotarget. 2018 Apr 13;9(28):19597-19612.

[3]. Ishii N, et al. Enhanced inhibition of ERK signaling by a novel allosteric MEK inhibitor, CH5126766, that suppresses feedback reactivation of RAF activity. Cancer Res. 2013 Jul 1;73(13):4050-4060.

U0126-EtOH | PD98059 | Trametinib (GSK1120212) | PD0325901 | Selumetinib (AZD6244) | Cobimetinib | PLX8394 | Doramapimod (BIRB 796) | PLX-4720 | LGX 818 | LY 3009120 | MEK162(ARRY-162,ARRY-438162) | GW5074 | RAF265 (CHIR-265) | AZ 628